There's apparently attempts from some of the high ups in Imagineering to accelerate construction and get it open MUCH earlier. I have no idea if they'll get their way. Though it always sort of struck me as strange to target an opening around winter. Florida may be sweltering throughout most of the year, but it still dips well into freezing temperatures during winter months. Even 40-50 degree weather is less than many people would want to ride it at.
Tiana is a rethemed ride, not a new one. Even if Disney isn't capable of quite the speedy pace they demonstrated in the 1900s, they should still be able to get this project done much quicker than their imposed deadline. IF they want to. Most of Disney's perceived sluggishness is intentional, spreading out costs over multiple quarters/years makes the books appear more attractive to the money people. They could go a lot faster if they want to. This probably applies to Tiana as well. Two years might seem speedy for their usual standards, but again it's still just a retheme of an existing ride. They used to get entire parks built within 2-3 years.